1. Field of the Invention
The present invention relates to a magnetic recording device for detecting microdefects in magnetic recording media.
2. Description of Prior Art
Magnetic recording devices are designed to record and reproduce information by rotating a magnetic disk composed of a ferromagnetic material and causing a magnetic head to scan over the magnetic disk and are generally used as auxiliary storage devices in computers.
With respect to data areas of magnetic recording medium of the magnetic recording devices, detection processing of defects is conducted during shipping from the production plant. The defect as referred to herein means the presence of scratches, contaminants, or particles on the surface of the magnetic storage medium. In the zones where defects are present, the degree of magnetization during writing is reduced and writing or reading is made difficult. The design is that the defect zone discovered in detection processing of defects during shipping from the production plant will be skip registered in the memory area of the processor that controls the magnetic recording device.
In the delivered magnetic recording devices, the zones where data is difficult to read or write during reading and writing of data are also skip registered. As a result, with respect to the defects that appeared after the delivery, the destruction of data that will be written into the zones of such defects can be prevented in advance.
Methods for writing and reading the usual data are considered as the conventional defect detection methods. Thus, the presence of defects can be detected by writing and reading the usual data and observing changes in the amplitude or phase of the signals that were read out.
FIG. 1 shows a signal that was read out during defect detection by writing and reading the usual data. In the zone DEF where a defect is present, the signal becomes discontinuous or the phase and amplitude change significantly. Detecting this zone makes it possible to detect the defect location.
Further, when the usual data is written or read, the data pattern is randomized, repetitions of “0” and “1” are restricted, and bit inversions that continue for a long time are rare.
Here, randomization is a processing conducted to eliminate the regularity of the write data. For example, a pattern with a repeating magnetization inversion, such that the data recorded on a medium is “1”, “1”, “1”, “1”, has a poor S/N ratio and a high error rate. Therefore, it is preferred that the occurrence thereof be reduced to a minimum. Accordingly, in the usual data writing, the processing for eliminating the regularity is conducted by using a scrambler.
FIG. 2 is an example of a scrambler for conducting randomization. A scrambler 100 comprises two exclusive OR (hereinbelow, ExOR) circuits 101a, 101b and a 10 bit shift register 102. Data X9-X0 stored in the shift register 102 are successively shifted from X0 to X9, the value of X9 and the value of X2 are inputted in the ExOR circuit 101a, and the output thereof is inputted as X0 in the shift register 102. Data BR prior to randomization is 8 bit parallel data; it is inputted in the ExOR circuit 101b together with the 8 bit data X2-X9 located in the shift register and is outputted as data AR after randomization from the scrambler 100. The scrambler 100 uses a 10 bit shift register 102 and, therefore, has a 1024 byte periodicity.
The technology described in Japanese Patent Application Laid-open No. H11-328877 represents a circuit for detecting defects in magnetic recording devices. With this technology, defect detection in a magnetic recording device is conducted by using usual data writing and reading.
However, all the defects are difficult to detect with the defect detection based on the usual data writing and reading. With the defect detection function provided in the conventional magnetic recording devices, the defects include microdefects that cannot be detected as rapid changes of phase or amplitude. Usually those microdefects in most cases can be repaired by an error correction function. However, the problem is that in the case where those microdefects have grown and increased in size, for example, due to changes in characteristics of head medium, the data discrimination capability of the location thereof is reduced, error correction capability is exceeded, and data restoration is impossible.